Magnetic media with randomly positioned texturing features

ABSTRACT

A magnetic data storage medium includes a dedicated transducing head contact zone for engaging an air bearing slider, primarily when the disk is stationary. The contact zone is textured with an irregular sequence of spaced apart nodules forming a substantially circumferential, spiral path. The spiral path includes multiple terms that define a uniform radial pitch. The circumferential pitch is irregular, more preferably determined according to pseudo-random function in which the actual spacing intervals vary about a nominal interval, over a range comparable to, but generally less than, the interval. The pseudo-random array can be formed by a texturing process that includes directing a focused laser beam onto the contact zone. The disk is rotated to maintain a constant circumferential speed relative to the laser, and also is translated radially to provide the desired radial pitch. The laser is operated in a continuous wave mode, with an acousto-optic modulator between the laser and disk operated to provide a pseudo-random variance in time intervals between successive laser exposures.

This application claims the benefit of Provisional Application No.60/041,067 entitled “Pseudo-Random Laser Texture to Reduce Head-DiscResonance during Take-off, Landing and/or Flying of the Head”, filedMar. 18, 1997.

BACKGROUND OF THE INVENTION

The present invention relates to texturing of magnetic data storagemedia, and more particularly to the texturing of dedicated transducinghead contact zones of such media to minimize system resonance.

Laser texturing of magnetic disks, particularly over areas designed forcontact with data transducing heads, is known to reduce friction andimprove wear characteristics as compared to mechanically textured disks.Traditional laser texturing involves focusing a laser beam onto a disksubstrate surface at multiple locations, forming at each location adepression surrounded by a raised rim as disclosed in U.S. Pat. No. 5,062,021 (Ranjan) and U.S. Pat. No. 5,108,781 (Ranjan). An alternative,as disclosed in International Publications No. WO 97/07931 and No. WO97/43079, is to use a laser beam to form domes or nodules, rather thanrims. In some cases, each of the domes is surrounded by a raised rim.The features can have either circular or elliptical profiles.

Collectively, the texturing features form a texture pattern ordistribution throughout the head contact zone. A particularly preferredpattern is a spiral, formed by rotating the disk at a controlled angularspeed while moving a laser radially with respect to the disk. The laseris pulsed to form the individual texturing features. For example, thedisk can be rotated to provide a circumferential speed of about onemeter per second. Then, operating the laser at 50,000 pulses per secondprovides a 20 micron circumferential pitch, i.e. distance betweenadjacent texturing features. The radial speed of the laser controls theradial pitch or spacing between adjacent turns of the spiral, which alsocan be about 20 microns.

Although this approach has been highly successful in terms of reducingdynamic friction and improving the wear characteristics of dedicatedtransducing head contact zones, the regular, repeating pattern of thelaser texture features produces strong input excitations based on thefundamental frequency of the circumferential pitch, including higherorder harmonics. When the excitation frequencies coincide with naturalfrequencies of the slider or its gimbal and support system, resonanceoccurs which results in a high amplitude acoustic energy signal, whichcan increase the difficulty of determining the glide avalanche breakingpoint (a disk/transducing head spacing value) and yield a falseindication that the disk has failed a glide test.

In addition to their resonance effects, regularly spaced apart texturingfeatures are thought to cause transducing head disturbances byintermittent contact of texturing-feature peaks with the datatransducing head during disk accelerations and decelerations. Also, thetexturing features contribute to turbulence in the air bearing thatsupports the transducing head slider during portions of accelerationsand decelerations. At close non-contacting proximity of the head,pressure modulation of the air bearing can induce head resonance.

Several previously proposed media texturing alternatives address thesedifficulties to a degree. For example, the aforementioned InternationalPublication Number WO 97/43079 includes the observation thatmechanically textured disks, as compared to laser textured disks,produce less acoustic energy during head take-off and landing. Anoise-reducing texturing alternative is discussed therein; namely, rowsof rims connected to one another at their ends, as shown in FIG. 15 ofthe publication. In U.S. patent application Ser. No. 09/381,079 now U.S.Pat. No. 6,229,670, entitled “Low Resonance Texturing of MagneticMedia”, filed Mar. 13, 1998, resonance-reducing texturing is disclosedin the form of elongate circumferential ridges, most notably acontinuous ridge in the shape of a spiral throughout the transducinghead contact region. Although both of these alternatives affordconsiderable reduction in noise during head take-off and landing, thereremains a need for noise-reducing texturing arrangements withsubstantial spacing between adjacent texturing features. Thesearrangements frequently are preferred to due to lower manufacturingcosts and better potential for producing a uniform roughness throughoutthe head contact zone.

Therefore, it is an object of the present invention to provide an arrayof texturing features adapted to impart a desired surface roughness tothe dedicated transducing head contact zone of a magnetic recordingmedium while minimizing undesirable resonant frequency effects.

Another object is to provide a magnetic data storage medium in which ahead contact zone has a topography comprised of multiple texturingfeatures in a pseudo-random array with irregular spacing intervalsbetween adjacent texturing features, at least in a selected directionalong the storage medium.

A further object is to provide a process for laser texturing a datastorage medium by subjecting the storage medium to intermittentexposures according to a pseudo-random sequence of timing intervalsbetween successive exposures, to cause an irregular spacing betweenadjacent texturizing features.

Yet another object is to provide magnetic data storage media thatexhibit the highly favorable dynamic friction and wear characteristicsof laser textured media, and further exhibit low resonance interactionswith transducing heads and their support structure during head take-offsand landings.

SUMMARY OF THE INVENTION

To achieve these and other objects, there is provided a magnetic datastorage medium. The medium includes a substrate body formed of anon-magnetizable material and a magnetizable film disposed over thesubstrate body. The recording medium has a substantially planar surfaceincluding a contact region adapted for a surface engagement with amagnetic data transducing head during accelerations and decelerations ofthe recording medium in a predetermined direction with respect to thetransducing head. Multiple texturing features are formed in the contactregion. The features protrude outwardly from a nominal surface plane ofthe substantially planar surface, and cooperate to define a surfaceroughness of the contact region. The texturing features are spaced apartfrom one another and arranged to define an irregular spacing betweenadjacent texturing features in the predetermined direction.

Preferably the texturing features are arranged to preserve a desireddensity (or permitted range of densities) as well as to provideirregular spacing. To this end, texturing features can be formed in asequence in which actual intervals between adjacent features vary abouta nominal spacing, and further vary about a range (maximum spacing lessthe minimum spacing) less than the nominal spacing. The nominal spacingcan be selected with the desired feature density in mind. In the mostpreferred arrangement, spacing intervals occur randomly throughout thepermitted range.

Typically the recording medium is a magnetic disk, with an annularcontact region. Then, the predetermined direction is circumferentialwith respect to the disk, and the irregular interval is thecircumferential pitch. A psuedo-random texture pattern throughout a headcontact region can be formed as a single, spiral sequence of texturingfeatures. The spiral provides essentially circumferential turns, with aselected, preferably constant radial pitch between adjacent turns.

The texturing features preferably are substantially uniform in theirdegree of extension away from the nominal plane, usually considered interms of height above a horizontal nominal plane. This imparts a desireduniformity to the surface roughness throughout the contact region. Thetexturing features, when formed as laser nodules or bumps, are roundedand substantially free of sharp edges, and have heights in the range ofabout 5-30 nm.

Further in accordance with the invention, there is provided a processfor surface texturing a magnetic data storage medium, including:

a. directing a coherent energy beam toward a magnetic storage medium;and

b. causing the coherent energy beam to impinge upon a selected surfaceof the storage medium at a plurality of different locations thereon,altering the topography of the selected surface at each location byforming a texturing feature, while selecting the locations to provide anirregular spacing between adjacent texturing features in at least onepredetermined direction along the selected surface.

When the data storage medium is a magnetic disk, texturing involves diskrotation to provide a circumferential velocity, in concert withcontrolling the rate or frequency of laser exposures. One suitableapproach involves rotating the disk to maintain a constantcircumferential speed, while varying the timing of laser energy exposureepisodes, either by controlling the laser itself or an optical componentintermediate to the laser and the disk.

In one preferred texturing arrangement, a laser operated in the CW(continuous wave) mode provides a beam directed through anaccousto-optic modulator, controlled by a pseudo-random pulse generator.The result is a pseudo-random sequence of texturing features thatcorresponds to the pseudo-random timing of the laser exposures. Whileother alternatives are conceivable, e.g., randomly varied disk rotation,considerably more precision is possible by varying the laser exposuretiming rather than disk movement.

A pulse laser, randomly triggered, can be used in lieu of the CW laserand accoustal-optic modulator combination, although it is felt to affordless precision by comparison to the preferred combination.

Thus in accordance with the present invention, the transducing headcontact zones of magnetic data storage media can be laser textured toform multiple spaced apart bumps or nodules that provide superior wearand friction characteristics, yet do not produce undesirable resonanceeffects during the take-offs and landings of transducing heads. Apseudo-random variance in spacing between adjacent texturing features,taken in the direction of medium/head relative movement, is particularlyeffective in reducing input excitations based on fundamental frequenciesand their harmonics resulting in improved media performance.

IN THE DRAWINGS

For a further appreciation of the above and other features andadvantages, reference is made to the following detailed description andto the drawings, in which:

FIG. 1 is a plan view of a magnetic data storage disk having apseudo-random texture array in accordance with the present invention,and a data transducing head supported for generally radial movementrelative to the disk;

FIG. 2 is an enlarged partial sectional view of the magnetic disk inFIG. 1;

FIG. 3 is a partial top plan view of a magnetic data storage disk with atexture pattern of discrete nodules according to the traditional lasertexturing approach;

FIG. 4 is a schematic representation of a surface profile of the contactzone in FIG. 3, taken in a circumferential direction;

FIG. 5 is a graph showing excitation amplitude as a function offrequency, with respect to the disk of FIG. 3;

FIG. 6 is an enlarged partial top plan view of the data storage diskshown in FIGS. 1 and 2, showing the textured head contact zone;

FIG. 7 is a schematic representation of a surface profile of the headcontact zone in FIG. 6, taken in a circumferential direction;

FIG. 8 is a chart showing excitation amplitude as a function offrequency, with respect to the head contact zone in FIG. 6;

FIG. 9 is a diagramatic view of a texturing system for forming thepseudo-random texture shown in FIG. 6;

FIG. 10 is a partial top plan view of an alternative data storage disktextured according to the present invention;

FIG. 11 is a sectional view of the disk in FIG. 10; and

FIG. 12 is a diagramatic view of an alternative embodiment texturingdevice.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to the drawings, there is shown in FIGS. 1 and 2 a mediumfor reading and recording magnetic data, in particular a magnetic disk16 rotatable about a vertical axis and having a substantially planarhorizontal upper surface 18. A rotary actuator (not shown) carriestransducing head support arm 20 in cantilevered fashion. A magnetic datatransducing head 22 (including magnetic transducer and air bearingslider) is mounted to the free end of the support arm, through asuspension 24 which allows gimballing action of the head, i.e., limitedvertical travel and rotation about pitch and roll axes. The rotaryactuator and the support arm pivot to move head 22 in an arcuate path,generally radially with respect to the disk.

At the center of disk 22 is an opening to accommodate a disk drivespindle 26 used to rotate the disk. Between the opening and an outercircumferential edge 28 of the disk, upper surface 18 is divided intothree annular regions or zones: a radially inward zone 30 used forclamping the disk to the spindle; a dedicated transducing head contactzone 32; and a data storage zone 34 that serves as the area forrecording and reading the magnetic data.

When the disk is at rest, or rotating at a speed substantially below itsnormal operating range, head 22 contacts upper surface 18. When the diskrotates at higher speeds, including normal operating range, an airbearing or cushion is formed by air flowing between the head and uppersurface 18 in the direction of disk rotation. The air bearing supportsthe head above the upper surface. Typically the distance between aplanar bottom surface 36 of head 22 and upper surface 18, known as thehead “flying height” is about 10 microinches (254 nm) or less. Lowerflying heights permit a higher density storage of data.

For data recording and reading operations, rotation of the disk andpivoting of the support arm are controlled in concert to selectivelyposition transducing head 22 near desired locations within data zone 34.Following a data operation, the disk is decelerated and support arm 20is moved radially inward toward contact zone 32. By the time the diskdecelerates sufficiently to allow head/disk contact, the head ispositioned over the contact zone. Thus, head contact with other regionsof the disk surface is avoided. Before the next data operation, the diskis accelerated, initially with head 22 engaged with disk 16 within thecontact zone. Support arm 20 is not pivoted until the head is supportedby an air bearing, above the contact zone.

Magnetic disk 16 is formed by mechanically finishing an aluminumsubstrate disk 38 to provide a substantially flat upper surface.Typically a nickel-phosphorous alloy has been plated onto the uppersurface of the substrate disk, to provide a non-magnetizable layer 40with a uniform thickness in the range of about 2-12 microns. Followingplating, the exposed upper surface 42 of the Ni—P alloy layer ispolished to a roughness of about 0.1 micro inch (2.54 nm) or less.

After mechanical finishing, substrate surface 42, at least along contactzone 32, is laser textured to provide a desired surface roughness. Lasertexturing involves melting the substrate disk at and near surface 42,forming texturing features as will be described in greater detail below.

Fabrication of disk 16 involves the application of several layers aftertexturing. The first of these is a chrome underlayer 44 with a typicalthickness of about 10-100 nm. Next is a magnetic thin film recordinglayer 46, where the data are stored, typically at a thickness of about10-50 nm. The final layer is a protective carbon layer 48, in the rangeof 5-30 nm in thickness. Layers 44, 46 and 48 are substantially uniformin thickness, and thus replicate the texture of substrate surface 42.

Laser texturing involves forming discrete nodules (also called bumps ordomes) in the substrate disk at surface 42. The size and shape of thenodules depends on the level of laser beam energy impinging upon surface42. Typically the nodules are formed in a spiral path, having acircumferential pitch governed by the disk rotational speed and laserpulsing interval during texturing. A radial pitch, i.e., the radialdistance between consecutive turns of the spiral path, is determined bydisk rotation and the rate of radial shifting of the laser relative tothe disk. The result of the traditional laser texturing, as seen in FIG.3, is a disk 47 having a textured head contact zone with a uniformcircumferential pitch, i.e., a uniform spacing or distance intervalbetween consecutive nodules 49. The nodules can be formed with a highdegree of uniformity in height (distance between the nodule peaks and anominal surface plane of the disk), typically in the range of about 5-30nm. This provides a uniform surface roughness, substantially throughoutthe contact zone. The surface profile view in FIG. 4 illustratescircumferential pitch.

This uniformity, however, when coupled with the uniform circumferentialpitch, leads to input excitation frequencies that vary linearly with thecircumferential speed of the disk relative to the transducing head.During transducing head takeoffs and landings, these input excitationfrequencies or their harmonics can coincide with natural resonantfrequencies of the transducing head or the head support structure,including the gimbal arrangement that allows adjustments in headorientation about mutually perpendicular pitch and roll axes. Theresonance effects are present during glide avalanche measurements, andcan provide an erroneous indication that a disk has failed a glide test,and make it difficult to determine the glide avalanche breaking point.The chart in FIG. 5, a plot of amplitudes (dB) with respect tofrequencies, illustrate high excitation amplitudes at the fundamentalfrequency and harmonics, with the magnitude of the spikes decreasing atthe higher frequencies.

FIG. 6 shows an enlarged part of contact zone 32 of disk 16. Nodules 51,actually formed as part of a continuous spiral, appear as a series ofhorizontal rows that correspond to the circumferential direction.Accordingly, circumferential pitch is represented by the horizontaldistances between adjacent nodules 51. The wide variety and randomnature of the spacing intervals is readily apparent. In the exampleillustrated, a pseudo-random texture has a nominal circumferential pitchof 45 microns, and the radial pitch is 25 microns.

In FIG. 7, a surface profile, taken in the circumferential directionalong a sequence of nodules, is placed adjacent a scale in microns, toillustrate the irregular nature of between-nodule spacing intervals.

Although the spacing between adjacent nodules is large in comparison tothe nodule size (5 micron modual diameters, for example), theinter-nodule spacing, both circumferentially and radially, is minute incomparison to the dimensions of transducing heads, which are typicallyexpressed in millimeters. Nonetheless, to maintain consistentperformance in terms of stiction and dynamic friction, it is desirableto maintain a density of nodules 51 at least similar to the density ofnodules 49 in the uniform pitch arrangement shown in FIG. 3.

To this end, spacing intervals are varied randomly about a nominalvalue. According to one example, the nominal circumferential pitch is 50microns, with spacings varied randomly throughout a range extending from30 microns to 70 microns, i.e., a 40-micron range. This range, whilesubstantial in comparison to the nominal spacing, is less than thenominal spacing.

The random or otherwise irregular spacing between consecutive nodulessubstantially reduces the amplitudes of input excitations. As seen fromthe chart in FIG. 8, which can be compared directly to the chart in FIG.5 concerning uniform nodule spacing, random spacing yields alow-amplitude spike at 30 kHz. Otherwise, the frequencies are spread outor smeared, i.e., substantially evenly distributed along a range offrequencies. Thus, randomizing the circumferential spacing effectivelyminimizes the input excitation.

FIG. 9 shows a laser texturing device 50 for forming pseudo-randomarrays of texturing features in accordance with the presence invention.Device 50 includes an Nd:YVO₄ diode laser 52, operated in the CW(continuous wave) mode. A beam 54 generated by laser 52 is provided toan acousto-optic modulator 56, which is controlled by a random pulsegenerator 58. The pulse generator consists of an arbitrary wave formgenerator (Tektronic/Sony AWG 2040) and a pulse generator (HP8116A).Beyond modulator 56, beam 54 proceeds through beam columnating andfocusing optics, represented by lenses 60, 62 and 64. The beam, emergingfrom lens 64, is focused on surface 42 of disk 16, at a beam impingementarea that typically is circular, but alternatively can have an elipticalor otherwise selectively shaped profile. The diameter of the impingementarea can vary with the application and optical components involved.

Focusing the laser energy onto the metallic surface of the substratedisk causes highly localized melting at the surface. Although thematerial resolidifies rapidly, there is sufficient material flow to forma nodule which projects outwardly, or to the left as viewed in FIG. 9,from the nominal surface plane.

The desired texture pattern or array is formed by rotating disk 16 usinga spindle 66, and radially translating the disk relative to the laserbeam, e.g., by a motor 68 operating on a shaft 70 to move a non-rotatingportion of spindle 66 upwardly and downwardly as viewed in the figure.To trace the preferred spiral path, disk rotation and radial translationoccur simultaneously. The degree of radial translation, with respect todisk rotation, determines the radial pitch or distance between adjacentturns of the spiral path.

A substantial departure from previous systems resides in the manner inwhich successive exposures of the disk to laser energy, i.e., successivenodule formation episodes, are timed.

Conventional laser texturing involves pulsing the laser at a uniformrate or frequency, e.g., 50,000 pulses per second, while maintaining aconstant circumferential disk speed, resulting in a uniformcircumferential pitch.

In contrast, modulator 56 is controlled to provide a pseudo-randomfrequency of nodule forming episodes, in which the actual intervalsbetween successive episodes varies about a nominal interval. Forexample, the interval between episodes (laser exposures) can vary over arange from 15 micro-seconds to 25 micro-seconds, about a nominalinterval of 20 micro-seconds.

The intervals between exposures are controlled by modulator 56. Moreparticularly, as controlled by pulse generator 58, modulator 56 eitherdirects beam 54 through the columnating and focusing optics, or divertsthe beam as indicated at 54(a). Thus, the modulator acts as a shutter,alternatively allowing and preventing laser exposure. This arrangementaffords precise control over the timing intervals, and thus enhances therandom nature of the variance in time intervals over the permittedrange. As mentioned above, a pseudo-random variance in exposures ispreferred. This is accomplished by use of a personal computer to programpulse generator 58 for pseudo-random timing.

FIGS. 10 and 11 illustrate an alternative embodiment data storage medium72, in particular a glass ceramic substrate 74 provided with a metalliclayer 76, e.g., chromium, sputtered or otherwise deposited onto theglass substrate. The metallic layer is exposed to a CW laser beam pulsedby a modulator while the substrate and metallic layer are rotated andtranslated radially, to form a texture array along a spiral path aspreviously described. To ensure that the topography is determined bynodule formation rather than by localized microfracturing, metalliclayer 76 should have a thickness of at least about 100 nm

FIG. 12 illustrates an alternative embodiment 78 for formingpseudo-random texture patterns. System 78 includes a pulsed diode lasercontrolled by a trigger signal 82 from a pseudo-random pulse generator(not shown). In response to each trigger, laser 80 generates a beam 84which proceeds through columnating and focusing optics 86 to a disk 88,which is rotated and radially translated as previously described. Thissystem, although it does not require an acousto-optic modulator, cannotbe controlled with the same precision as the system shown in FIG. 9.

Regardless of whether the system in FIG. 9 or the system in FIG. 12 isemployed, the preferred approach is to form the sequence of nodules in aspiral path, since the texturing of the entire head contact zone can becompleted in one, continuous operation. However, either system can beused to form other pseudo-random arrangements of the texturing features,e.g., a series of concentric rings with a uniform radial pitch and arandomly varied circumferential pitch within the rings.

Thus, in accordance with the present invention, the transducing headcontact zones of data storage disks are textured to provide an enhancedsurface roughness that improves dynamic friction and wear, yet alsovirtually eliminates the problem of input excitation frequencies thatyield unduly high acoustic energy signals during the take-off andlanding of the head slider. This result is achieved by providing apseudo-random or otherwise irregular arrays of nodules or othertextizing features, in particular, sequences in which the spacingbetween adjacent nodules varies in the circumferential direction. Thenodules can be arranged in highly random arrays, yet nonethelesspreserve the desired densities for favorable stiction and frictioncharacteristics, for considerably enhanced media performance.

What is claimed is:
 1. A magnetic storage medium including: anon-magnetizable substrate having a substantially planar substratesurface including a selected region for supporting contact of a magneticdata storage medium including the non-magnetizable substrate with amagnetic transducing head during accelerations and decelerations of thesubstrate in a predetermined direction with respect to the transducinghead; and multiple texturing features in the selected region, protrudingoutwardly from a nominal surface plane of the substrate surface andcooperating to define a surface roughness of the selected region,wherein the texturing features are spaced apart from one another andarranged to define an irregular spacing between adjacent texturingfeatures in the predetermined direction; wherein intervals of spacingbetween adjacent texturing features in the predetermined direction varyabout a nominal spacing, and over a range (maximum spacing less minimumspacing) less than the nominal spacing.
 2. The storage medium of claim 1wherein: the substrate is disc shaped, the selected region is annular,and the predetermined direction is circumferential with respect to thesubstrate.
 3. The storage medium of claim 2 wherein: the texturingfeatures are formed in a single spiral path, and the spacing betweenadjacent features along the spiral path varies randomly.
 4. The storagemedium of claim 2 wherein: the texturing features form multiplecircumferential rings radially spaced apart from one another, with acircumferential spacing between adjacent features in each of the ringsbeing randomly varied.
 5. The storage medium of claim 1 wherein: thetexturing features are substantially uniform in their height above thenominal plane.
 6. The storage medium of claim 1 wherein: the texturingfeatures have heights above a nominal plane in the range of from aboutfive nanometers to about 30 nanometers.
 7. The storage medium of claim 1wherein: the texturing features are rounded and substantially free ofsharp edges.
 8. The storage medium of claim 1 wherein: the texturingfeatures cooperate to form side-by-side rows, each row extending in thepredetermined direction.
 9. The storage medium of claim 1 wherein: themultiple texturing features are spaced apart from one another accordingto a pseudo-random variance of the spacing.
 10. The storage medium ofclaim 9 wherein: the nominal spacing is greater than a nominal size ofthe texturing features by approximately a factor of ten.
 11. The storagemedium of claim 1 further including: at least one thin film layerdisposed over the substrate surface and defining a substantially planarouter surface including a contact region over the selected regionadapted for a surface engagement with the magnetic data transducing headduring the accelerations and decelerations of the substrate.
 12. Thestorage medium of claim 11 wherein: the at least one thin film layer issubstantially uniform in thickness whereby the outer surface tends toreplicate the substrate surface.
 13. The storage medium of claim 11wherein: the at least one thin film layer comprises a metallicunderlayer disposed over the substantially planar substrate surface, anda magnetic thin film recording layer disposed over the metallicunderlayer.
 14. A magnetic data storage medium, including: anon-magnetizable substrate having a substantially planar substratesurface defining a nominal surface plane and including a selectedregion; multiple texturing features in the selected region, protrudingoutwardly from the nominal surface plane and cooperating to define asurface roughness of the selected region, wherein the texturing featuresare spaced apart from one another to form at least one row of thetexturing features extending in a predetermined direction, with anirregular spacing between adjacent texturing features in said at leastone row; and at least one thin film layer disposed over the substratesurface and defining a substantially planar outer surface including acontact region over the selected region adapted for a surface engagementwith a magnetic data transducing head during accelerations anddecelerations of the substrate in said predetermined direction withrespect to the transducing head, the thin film layer being substantiallyuniform thickness whereby the outer surface tends to replicate thesubstrate surface; wherein intervals of spacing between adjacenttexturing features in the predetermined direction vary about a nominalspacing, and over a range (maximum spacing less minimum spacing) lessthan the nominal spacing.
 15. The medium of claim 14 wherein: thesubstrate is disc shaped, tile contact region is annular, and thepredetermined direction is circumferential with respect to thesubstrate.
 16. The medium of claim 15 wherein: the at least one row oftexturing features forms a spiral path, and the spacing between adjacentfeatures along the spiral path varies randomly.
 17. The medium of claim15 wherein: the at least one row of texturing features comprise multiplecircumferential rings radially spaced apart from one another, wherein acircumferential spacing between adjacent texturing features in each ofthe rings is randomly varied.
 18. The medium of claim 14 wherein: the atleast one row of texturing features comprises a plurality of said rowsextended in the predetermined direction.
 19. The medium of claim 14wherein: the texturing features are substantially uniform in theirheight above the nominal surface plane.
 20. The medium of claim 14wherein: the texturing features have heights above the nominal surfaceplane in the range of from about five nanometers to about thirtynanometers.
 21. The medium of claim 14 wherein: the texturing featuresare spaced apart from one another according to a pseudo-random varianceof the spacing.
 22. The medium of claim 21 wherein: the nominal spacingis greater than a nominal size of the texturing features byapproximately a factor of ten.
 23. The medium of claim 14 wherein: theat least one thin film layer comprises a metallic underlayer disposedover the substrate surface and a magnetic thin film recording layerdisposed over the metallic underlayer.
 24. The medium of claim 23wherein: the at least one thin film layer further comprises a protectivecarbon layer disposed over the magnetic thin film recording layer.
 25. Amagnetic data storage device, including: a non-magnetizable substratehaving a substantially planar substrate surface defining a nominalsurface plane; multiple texturing features formed over at least aselected region of the substrate surface and arranged in a plurality ofrows extending in a predetermined direction, with an irregular spacingbetween consecutive texturing features in each of the rows; and a thinfilm layer disposed over the substrate surface, defining an outersurface that tends to replicate the substrate surface, the outer surfaceincluding a contact region over the selected region adapted for surfaceengagement with a magnetic data transducing head during accelerationsand decelerations of the substrate in the predetermined direction withrespect to the transducing head; wherein intervals of spacing betweenadjacent texturing features in the predetermined direction vary about anominal spacing, and over a range (maximum spacing less minimum spacing)less than the nominal spacing.
 26. The device of claim 25 wherein: thesubstrate is disk shaped, the contact region is annular, and thepredetermined direction is circumferential with respect to thesubstrate.
 27. The device of claim 26 wherein: the rows of texturingfeatures form respective portions of a spiral path, and the spacingbetween the consecutive features along the spiral path varies randomly.28. The device of claim 26 wherein: the rows of texturing featurescomprise respective circumferential rings radially spaced apart from oneanother, wherein a circumferential spacing between the consecutivetexturing features in each of the rings is randomly varied.
 29. Thedevice of claim 26 wherein: adjacent ones of the rows are spaced apartby a substantially constant radial pitch.
 30. The device of claim 25wherein: the texturing features project outwardly from the nominalsurface plane of the substrate surface and cooperate to define a surfaceroughness of the selected region.
 31. The device of claim 30 wherein:the texturing features are substantially uniform in their height abovethe nominal surface plane.